1. Field of the Invention
The present invention relates to a vehicle lamp utilizing a plurality of light emitting diodes as light sources, each light emitting diode including a lens portion whose function is divided into direct light area and reflected light area in order to facilitate control of luminous distribution, which enables the luminous distribution control with a reflective mirror arranged around the light emitting diode so as to eliminate need of providing the lens steps.
2. Description of the Related Art
Among a number of light emitting elements, light emitting diodes which have undergone steady luminous flux enhancement are now used in various display units as it is advantageous to use such light emitting diodes in view of increasing the life and power-saving and decreasing the calorific value in comparison with conventional light sources such as incandescent bulbs. With respect to application of light emitting diodes to vehicle lamps, for example, there may be enumerated high mounted stop lamps, side marker lamps and tail stop lamps for preventing motoring accidents caused by rear-end collisions.
More specifically, a light emitting diode has a semiconductor chip (light emitting chip) inside and the chip is protected by a transparent resin-made lens portion. Further, the front end portion of the lens portion has a spherical surface that is rotationally symmetric around the optical axis. Consequently, luminous intensity distribution of a single element is substantially close to the frustrum of a circular cone, whereby the tendency is for the luminous intensity to become high in the central portion near the optical axis on one hand and for the luminous intensity to become lower as the distance between the optical axis and the peripheral portion increases on the other.
As luminous distribution is designed by utilizing only the direct light of a light emitting diode in a lighting device using a conventional light emitting diode, it is needed to use lens steps (fish-eye lens steps) for the light control. In other words, there exist problems arising from difficulty in fully utilizing light contributing to desired luminous distribution unless some lens element is provided in front of the light emitting diode and from a limitation in designing the external appearance due to the formation of the lens steps.
Further, it is important whether the configuration of the lens portion of the light emitting diode is symmetric around the optical axis. In other words, the following inconvenience is caused by making the configuration of the front end of the lens portion rotationally symmetric (a rotator such as a spherical surface) in the conventional LED.
FIG. 14 is a conceptual isoluminous intensity distribution map in the conventional LED, showing a concentric circular pattern arrangement (i.e., isoluminous intensity curves form substantially concentric circles) due to the lens portion in the form of a rotator. Therefore, assuming that a long-sideways range (see a range R indicated by a rectangular frame of a chain line in FIG. 13) with the width in the lateral direction (see Hxe2x80x94H line) being greater than the width in the vertical direction (see Vxe2x80x94V line), for example, useless light is generated in the upper and lower portions and this causes loss of light that is unrelated to the luminous distribution standard. The light is due to the contribution made only by direct light from the chip of the LED. Accordingly, in order to utilize light without waste, the lens steps (fish-eye lens steps) disposed in front of the LED plays an important part in controlling luminous distribution in the conventional arrangement. However, the problem is that the provision of such lens steps is disadvantageous in view of cost-saving and any restriction imposed on design-making.
Moreover, when a light emitting diode is used as a light source for a lighting device, there are known methods including: utilizing the light directly emitted from the light emitting diode as irradiation light; and providing a reflective mirror around the light emitting diode whereby to utilize not only the light reflected from the reflective mirror but also the light directly emitted from the light emitting diode. In the case of the latter, a reflective mirror having a paraboloid of revolution is employed.
However, use of only the reflective mirror having the paraboloid of revolution is unable to fully satisfy the luminous distribution required for a vehicle lamp and in order to meet such a requirement, light is needed to be diffused from right to left by the function of lens steps.
In other words, a light emitting diode generally has a semiconductor chip (light emitting chip) inside and the chip is protected by a transparent resin-made lens portion (sealing lens). Further, the front end portion of the lens portion has a spherical surface which is rotationally symmetric around the optical axis of the lens portion. Consequently, luminous intensity distribution of a single element is substantially close to the frustrum of a circular cone, whereby the tendency is for the luminous intensity to become high in the central portion near the optical axis on one hand and for the luminous intensity to become low as the distance between the optical axis and the peripheral portion increases on the other.
However, there exist problems such as an increase in cost due to the processing cost for the formation of the lens steps as described above, loss in the quantity of light by passing through the lens steps, and a limitation in designing the external appearance due to the formation of the lens steps.
An object of the present invention is to obtain a desired luminous distribution without the help of the function of any optical element other than direct emission and reflection by utilizing the light emitted from a light emitting diode with efficiency.
In order to solve the foregoing problems, a light emitting diode having a light emitting chip and a lens portion for containing the chip of which lens portion has the divided areas such as a direct light area for use in directly emitting the light emitted from a chip outside as direct light and a reflected light area for use in emitting the light emitted from the chip and passed through the lens portion toward a reflective member provided outside the lens portion.
Further, the front end portion of the lens portion is used as a direct light area and the area is formed so that it has a configuration irrotationally symmetric around the optical axis of an element, and the peripheral portion of the direct light area or the side portion of the lens portion is used as the reflected light area and the area is formed so that it has a configuration rotationally symmetric around the element.
In a vehicle lamp according to the invention, a plurality of light emitting diodes thus structured are arranged so as to form a group of light sources on a support member and reflective mirrors are disposed in a manner surrounding the respective light emitting diodes. The light emitted from the chip of the light emitting diode is passed through the direct light area before being directly emitted outside and the light emitted from the chip and passed through the reflected light area is emitted toward the reflective mirror disposed with respect to the light emitting diode and reflected therefrom.
With respect to control of light from the light emitting diode according to the invention, the light directly emitted outside the lens portion through the direct light area is differentiated from the light reflected from the reflective member (or reflective mirror) through the reflected light area, so that each ray of light can be utilized effectively on an objective basis regarding contribution to luminous distribution accordingly.
Another object of the present invention is to utilize the light emitted from a light emitting diode with efficiency without the help of the function of any optical element other than direct emission and reflection in a vehicle lamp using a light emitting diode.
In order to solve the foregoing problems, the following arrangement is taken into consideration.
As to the light emitted from a light emitting diode, the light reflected at a position close to the peripheral edge of the opening of the reflective mirror annexed to the light emitting diode is emitted in a direction substantially parallel to the optical axis of the reflective mirror.
On the other hand, the very light reflected at a reflecting point closer to the optical axis of the reflective mirror has an increased angle with the optical axis and is emitted in a direction crossing a plane (including the optical axis) intersecting a plane including the reflecting point and the optical axis at right angles.
Consequently, according to the invention, luminous distribution required for a vehicle lamp can be acquired due to the optical function of the reflective mirror affixed to the light emitting diode without necessitating the refracting function of lens steps.